Bug report: using git commit-tree with "-F -" adds trailing newlines

I believe I've stumbled across an inconsistency in how git commit-tree reads messages from stdin. I would expect the behavior of these two commands to be identical, and that neither would actually change any commits:

    git filter-branch --commit-filter 'git commit-tree $@'
    git filter-branch --commit-filter 'git commit-tree -F - $@'

(If that assumption is untrue, please feel free to correct me and disregard the rest of this message.)

What I'm observing is that if I add a commit with a message that doesn't end in a trailing newline, like this:

    git merge `echo -n "No trailing newline" | git commit-tree
HEAD^{tree} -p HEAD`

Then I get different behavior in different versions of Git on different platforms. On git 1.8.4 on Ubuntu 12.04 (build from https://launchpad.net/~git-core/+archive/ppa) under GNU bash, version 4.2.25(1)-release (x86_64-pc-linux-gnu), using "-F -" seems to add a linefeed to the body:

    $ git log -n 1 --format=:%H:%B:
    : 4a11052c110c3daea46c89ae1118b1a2c59cc01b:No trailing newline:
    $ git filter-branch --commit-filter 'git commit-tree $@'
    Rewrite 4a11052c110c3daea46c89ae1118b1a2c59cc01b (2/2)
    WARNING: Ref 'refs/heads/master' is unchanged
    $ git filter-branch --commit-filter 'git commit-tree -F - $@'
    Rewrite 4a11052c110c3daea46c89ae1118b1a2c59cc01b (2/2)
    Ref 'refs/heads/master' was rewritten
    $ git log -n 1 --format=:%H:%B:
    :5ecba0ff0ca1290f2a5e3a599622e2a59e311f67:No trailing newline
    :

On git 1.7.12.4 (Apple Git-37) on Mac OS X 10.8.5 using GNU bash, version 3.2.48(1)-release (x86_64-apple-darwin12), both commands (with and without the "-F -" add newlines to the body of the commits.

Thanks for your attention!

Mick